Short wave converter



Jufie'S, 1937.

V H. M. LEWIS SHORT WAVE CONVERTER Original Filed Sept. 25, 1951 5 Sheets-Sheet 1 i lrwkm INVENTOR Harald [1197/92 lei-W5 zuiuuum .iqucqomm 605mm WW BY M)- W ATTORNEYS I IIIIIIETHLII |-||||e w ww June 8, 1937.

H. M. LEWIS SHORT WAVE CONVERTER Original Filed Sept. 25 1951 3 Sheets-Sheet 2 INVENTOR Harold /V///zr [cw/s BY 0 7 16M Map 1 ATTO R N EY5 June 8, 1937. Re 20,400 H. M. LEWIS SHORT WAVE CONVERTER Original Filed Sept. 25 1931 5 Shets-Sheet 5 51 lea? INVENTOR I #07021 /r Ze ls fiw, Me M ATTORNEYj Reissued June 8, 1937 UNITED STATES 25 Claims.

The present invention relates to a tuning system, or, more particularly, to such a system for use in a short wavereceiving apparatus. Exemplary of such a system is that used in a short wave converter.

A short wave converter is an apparatus which, when used in conjunction with any broadcast receiver, permits the reception of short wave signals by the said broadcast receiver. The con- 0 verter comprises an oscillator and modulator, by

which the short wave signal currents are converted into currents of a frequency within the tuning range of the broadcast receiver. The current of this frequency, which frequency will be referred to hereinafter as the intermediate frequency, is amplified, detected and reproduced by the broadcast receiver.

The frequency range covered by the short wave band is approximately from 1500 kc. (200 meters) to 20,000 kc. (15 meters). This range of frequencies is so great that it is not practical to tune a circuit through the entire range by the variation of a single tuning element. Some arrangement must be provided for changing both of the frequency determining elements; .that is, both the inductance and the capacity. In ac-' cordance with the usual practice thetuning is actually done by varying the capacity of a variable condenser, and the inductance is changed in steps to permit the condenser to tune the circuit throughout the various portions of the range.

It is common practice to divide the short wave band into several bands which will be referred to in this application. as the short wave band, the middle; wave band, and. the long wave band.

, The inductances used in tuning the radio frequency circuits of the short wave receiver, or the 4" radio frequency circuit and oscillator circuits of a converter, are usually wound on removable forms commonly known as plug-in coils, which coils are changed when desiring to go from one of the short wave bands to another. A system'ot this type has the disadvantages that it is expensive to manufacture and req e shifting of coils when operating.

Various systems havebeen proposed by which the inductance of the tuning coils is changed in steps by means of switches. However, the leads and switch mechanisms introduce capacities which considerably lessen the range of the tuning condensers, and usually the resulting large number of points to be switched has condemned this system. Furthermore, when the inductance PATENT OFF-ICE snon'r wave oonvea'raa Harold Miller Lewis, Great Neck, N. Y., assignor to Hazeltine Corporation Original No. 2,001,277, dated May 14, 1935, Serial- No. 565,024, September 25, 1931. Application for reissue April 2, 1937, Serial of the tuning coil is changed in steps by means of switches, the tuning condenser is no longer effective to tune the circuit in correspondence with other tuned circuits of the receiver which are controlled by the same control means.

Furthermore, considerable difficulty is experienced in constructing an oscillator capable of covering such abroad range of frequencies, as there is a considerable difference in the feedback coupling 'needed at the two ends of the short wave band. I V

It is the object of the present invention toovercome the above noted difficulties and provide a system in which the inductance values may be varied in steps by providing a system in which the leads required for changing the inductances are relatively short and have negligible capacity effects. It is a further object of this invention. to provide an oscillator coupling system having a simple structure, not involving the use of moving parts, by which the coupling effect may be simultaneously altered as the frequency determining inductance is changed, to permit the oscillator to oscillate effectively throughout the entire short wave band.

It is a further object of the invention to provide an oscillator coupling system in which the inductance of the frequency-changing circuit is changed in steps to effect large changes in the oscillation frequency and in which ameans is provided for simultaneously varying the tuning characteristic of the circuit to correspond with the tuning characteristic of the other tuned circuits of a receiver.

These and further objects of this invention will become apparent from the following speci fication taken in connection with the appended claims and drawings.

In one'embodiment of the present invention .the inductance of the frequency determining circuit of the converter oscillator is provided with a switch for short-circuiting the long wave portions thereof and long wave and middle wave portions thereof, when operating the oscillator to receive signals in the middle wave band and short wave band, respectively. Dual magnetic and capacitative feed-back couplings are provided between the plate circuit of the oscillator and the grid coil when operating within the middle wave band. When operating in the long wave band the inductive coupling is negligible,'and the feed-back is essentially through the capacitative coupling between the plate and grid circuits. When operating'in the short wave band the capacitative coupling effect becomes negligiinput of the modulator.

ble, whereas the coupling between the circuits due to the inductive coupling, is considerable.

Provision is also made for obtaining a uniform coupling between the antenna circuit and the A straight inductive coupling is utilized when receiving signals within the short wave and middle wave band. When operating in the long wave band an auto transformer eiIect is obtained by connecting the an tenna circuit to include a portion of the long wave section of the grid inductance.

The modulator and oscillator windings are so arranged relative to the switches for short-circuiting their unused portions and relative to the grids of the modulator and oscillator tubes that the leads, particularly when the converter is operating in the short wave band, are as short as possible.

In order to permit the continuous rotation of the tuning dial in either direction to progressively tune the converter through the entire band, the condensers used in both the modulator input and oscillator circuits are each rovided with double stators and double rotors 'o constructed that when the capacity between one of the pair of rotors and stators is maximuimthat between the-other pair of rotors and stators is minimum.

Switching means are provided, operated s'imultaneously with the switches for short-circuiting the unused portions of the tuning inductances, for connecting the appropriate sections of the condensers.

Series condensers are provided for connection in the oscillation circuit for each of the bands and are appropriately connected in circuit by a switch operated together with the previously mentioned switches, when the range of-the converter is shifted from one band to the other. The padding condensers for the section of the oscillator tuning condenser, which is used for the middle wave band, is provided in shunt with this section. A condenser is connected from the middle wave band tap of the inductance to the stator of the condenser, so that when the entire tuning inductance is in use this condenser may act as a padding condenser for the long wave band. This condenser is then essentially in shunt with the section of the variable condenser in use.

When the long wave section of the inductance is short-ci'rcuited, however, as when operating in the middle wave band, this condenser is in garallel with the series condenser in use at that me. i

The condenser shaft has an indicator dial geared thereto so arranged that it rotates a complete revolution for each half revolution of the condenser shaft. This dial has thereon three indicating scales, the outer scale being for indicating the frequencies in the short wave band, and the inner scale being for indicating the frequencies, in the long wave band. The scales pass by indicator lights placed behind the dial within a compartment which permits illumination of but a single scale by eachlamp, and a switch operated simultaneously with the wave changing switches operates to light the appropriate scale. A full description of this feature of the present invention is given in an application of Hamid Miller Lewis for Tuning scale, Serial No. 565,027, filed September 25, 1931, Patent No. 1,987,857 dated January 15, 1935.

In order to permit the operation of a single control knob to control the frequency of reception, regardless of which of the three bands the converter is operating in, there is provided a operation of a single control, and by which the frequency for which this apparatus is set to respond is automatically indicated at all times as the set is tuned.

In order to prevent the reception of'broadcast signals by the receiver used in conjunction with the converter, the leads between the converter, as well as the converter itself, are completely shielded. The antenna input of the converter contains a trap circuit to prevent currents of undesired frequency being impressed upon the input of the modulator and amplified thereby. The plate supply'of the modulator contains a tuned radio frequency choke whichv is tuned roughly to the intermediate frequency and thereby tends to bypass currents of frequencies diifering greatly therefrom which have been received in the converter. The full details of this .portion of the present invention are given in U. S. Patent No. 2,000,084, issued May 7, 1935, on an application of Harold Miller Lewis for Short wave receiver arrangement, Serial No. 565,025, filed "'c'oncurrently with the'original application.

Attention is now invited to the accompanying drawings in which:

Fig. 1 is a circuit diagram of the converter embodying the present invention;

Fig. 2 is a simplified circuit diagram of the converter circuit as connected when the switch is in the long wave position;

Figs. 3 and 4 are elementary diagrams for use 7 includes the antenna H), the ground II, the trap circuit l2, comprising the inductance l3 and condenser M, the primary winding l5, and a portion of the secondary winding It. The inductance l3 and the condenser [4 of the trap circuit I2 are so proportioned that said circuit is resonant to the intermediate frequency produced by the short wave converter. The input circuit of the converter isconnected to the grid of modulator device I1, which may be any thermionic tube, though that shown is of the screen grid type. The input circuit is tuned by means of the condenser I, which may be a double condenser employing, as shown, a single rotor and two stators so arranged that the capacity obtained between the rotor and one stator is maximum, when the capacity between the rotor and the other stator is minimum. The connections to the stators-are controled by means of the switch 23. The actual condenser includes two'stators and two rotors, so arranged that when one rotor is entirely within its-stator, the other rotor is'entirely out of its stator. The function of the condenser and switch arrangement. will be explained later.

used portions of the winding are The tapped secondary I6 is connected by means of switch 24, so that any of the tapped portions of the secondary may be included in the input circuit. The switch is so connected that the unshort-circulted.

For producing the heterodyhedrequency for combining with the incoming signal and thus producingthe intermediate frequency, there is provided the oscillator 25. This oscillator tube is of the single grid type and includes in its grid circuit the secondary 40 of the oscillation transformer, the primary 42 of which is connected in the plate circuit which includes stopping condenser 43. The secondary 40 is a tapped winding similar to 18 of the antenna transformer, and the connections to said secondary are controlled by means of switch 34. Thegrid return of the oscillation circuit is completed through the biasing resistor 21, which is connected to the cathode of the tube 25. The frequency of the oscillation circuit is determined by means of condenser 3|, which is similar to condenser 2 I and is connected to be operated therewith in a. uni-control manner by means of the control knob 22 with the indicator dial 25.

The connections to the two continuously variable portions of the condenser 3| are controlled by means of switch 33.

Padding condensers 4 IM across the two portions of condenser, as shown, for the purpose of aligning the oscillation circuit with the input of modulator H in the middle wave range and short wave range, respectively. Padding condenser 4IL is connected across the long wave portion'of the inductance winding 40, so that when the switch 34 is on contact L this condenser is practically in shunt with the condensers 3| and HS for adjusting the alignment inthe long wave range. When the switch 34 is on contact M, the condenser 4|L is in shunt with condensers 31 and 31', and the total series capacity is at that time the sum of these three condensers.

In series with condenser 3| is provided a series capacity which is variable in steps, comprising condensers 35, 31 and 38, the connections to which are controlled by means of the switch 35. Each of these condensers is provided with the padding condenser 36', 31', or 38', respectively, for the purpose of correcting the alignment of oscillator circuit with the modulator input in the various frequency bands. In the middle frequency band, as has-just been stated, the condenser 4 IL is in shunt with 31 and 31'. Coupling coils 44 and 45 coupled to the middle and long wave portions of the secondary 40, respectively, are included in the cathode circuit of the modulator I1. This circuit also includes the biasing resistor 45 shunted by by-pass condenser 41 for the purpose of causing tube H to actas a modulator.

and MS are provided The plate and screen grid potential are provided by means of the power supply source 20 which, as shown, is of the ordinary double wave rectifier and filter type. This power supply also provides heater lighting current for heating the cathodes of tubes 11 and 25. A resistor 29 is included in the plate lead of the oscillator 25 for the purpose of reducing the plate potential thereof.

As shown, the dial 25 includes three scales, 25-41, 25-b, and 2G--c, these scales covering the short wave band, middle wave band, and

long wave band, respectively.

It is to be noted that in order to get better 5 spacing. of the frequency indicators, the short associated wave scale is placed in the outer position on the dial 25, as the condenser motion to get the frequency separation required to separate the various stations isless in the short wave band than it is in the long wave band.

For the purpose of indicating in which of the frequency ranges the converter is operating, each of the scales is provided with one of the illuminating lights 1|-a 1|-b, or 1|-c, controlled by means of switch 39 to light them when tuning through the short wave band, middle wave band, and long wave band, respectively.

Switches 23, 24, 33, 34, 35 and 39 are so arranged as to be simultaneously operated and also to be actuated by the control knob 22 as the condensers are tuned through the limiting capacities for one of the frequency bands. Thus, the rotation of the control knob 22 results in the actuation of the ing of the connections to condensers 2| and 3|, respectively, to give the opposite capacity extreme for the modulator and oscillator circuits. Switch 38 is simultaneously operated changing the lighting of the indicating lights and thus indicating the change in the frequency band by changing the indication from one to another of the scales. The specific means for actuating the switches constitute no part of the present invention.

Included in the plate supply to the modulator I1 is the inductance 50. This inductance may have a high inherent capacity as indicated by capacity 5|, or an actual condenser may be placed in shunt therewith. The inductance and capacity, however, are so proportioned that frequencies other than the desired intermediate frequency will be by-passed.

A connection from the output of modulator I1 is made through condenser 52 and lead 53 to the antenna binding post of the receiver 51. This connection is made through a shielded cable 54, which may, for example, be a BX cable, from the walls of which the lead 53 is spaced by means of bakelite spacers 56. Also connected through the cable 54 is the ground connection 55, which is connectedto the ground binding post of receiver 51. The capacity 52 and the inherent capacity between the leads 53 and 55 are so proportioned that they constitute a dummy antenna to properly load the modulator l1, and to prevent misalignment of the input of receiver 51. Switch 59 is provided between the antenna I0 and the lead 53 by means of which the antenna may be directly connected to the input of the receiver 51 when it is desired to receive signals in the broadcast band directly on receiver 51.

The receiver 51 may be of any well known type, and is provided with the usual sound reproducing device 58. The specific details of neither 51 nor 58 constitute any part of the present invention.

The receiver is tuned to the intermediate frequency which it is desired to utilize, preferably .000 kc. The direct reception of signals of 1,000 kc. when the set is being operated to receive short wave signals by means of the converter, is prevented by means of the shielded cable 54. The modulator is prevented from acting as an amplifier of signals of 1.000 kc. frequency by means of trap circuit l2. Any signals of a frequency other than 1,000 kc. in the output of modulator l1 would be by-passed through the inductive 50. It is thus seen that a number of provisions have been made to prevent the interference of broadcast. sigby means of the converter.

In Fig. 2, to which attention is now invited, the circuit shown in Fig. 1 is again represented, except that the switches have been eliminated, the connections being made as if the converter were tuned to some frequency within the long wave band. In this circuit the high potential is represented as being supplied by means of the directcurrent source 80, and the screen grid potential of the'device I1 is obtained therefrom by including a resistor 8| in the screen grid circuit. The output of the oscillator circuit herein represented as 83 is fed to the cathode lead of the modulator I! which, as has been described, is biased for grid bias detection. The incoming signal is fed through the oscillatory circuit 84 to the input ,of tube l1, which by means of the biasing resistor 46 operates as a rectifier or modulator, and thereby produces in its output circuit a distorted wave form from which a current of the intermediate frequency can be selected and supplied through the condenser 52 to the terminals A and G of the radio broadcast receiver.

It is to be noted that frequencies other than the intermediate frequency for which the radio broadcast receiver is to be adjusted are by-passed through the inductance 50, whereas this inductance and its inherent capacity form a high impedance path relative to currents of the intermediate frequency.

As previously stated, the circuit l2 acts to prevent currents of the intermediate frequency being received over the antenna I0 and amplified by the modulator l1, and the shielding of the lead 53 prevents a direct pick-up between the output of the device i1 and the input of the radio broadcast receiver.

The oscillator circuit 83 contains, as can be seen, the usual series condenser v38 in series with the tuning condenser 3|, by means of which the circuit 83 is made to respond to a frequency con tinuously differing from the frequency to which circuit 84 responds by the amount of the intermediate frequency as the circuits are tuned in a uni-control manner.

Figs. 3 and 4 illustrate the means .by which the single oscillation transformer is made to cover the considerable frequency range required of this type of equipment. The various portions of the inductance 40 are tuned by the respective parts of the condenser 3| and thus constitute a tuned grid circuit.

In order to provide the offset frequency and thus permit alignment betweenthe' condensers 3| and 2| to permit ganging, a series condenser 36, 31 or 38 is provided. This condenser has the dual function of assisting the alignment and of permitting capacitative feed-back action. The introduction of this capacity in the grid return requires a resistor 21 to prevent the grid from fioatingand to act as a grid bias resistor.

More specifically, Fig. 3 shows the action on the circuit when it is operating in the short wave and middle wave band. The used portion of the inductance 40 in these bands is relatively small and there is considerable coupling effect between the feed-back inductance l2 and inductance III. This is particularly true in the short wave band.

In the short wave band the capacitative feedback coupling is negligible. In the middle wave band, however, the capacitative feed-back action I is considerable. The inductive feed-back action between 42 and 40 is less within this range, and the two couplings .are so arranged as to give practically uniform operation throughout the middle frequency band.

Referring particularly to Fig. 4, in which the circuit represents the action of the oscillator circuit when operated in the long wave band, the inductive coupling between the coils 42 and 40 is negligible, and the oscillator is of the capacity coupled type utilizing the series capacity 38.

Fig. 4 also represents the padding capacity arrangement. As can be seen from Fig. 1, the same section of the condenser 3| is utilized throughout the long and short wave bands. This complicates the arrangement required for the padding capacity in these two bands. The usual padding condenser HM, however, is provided for the middle frequency band. The usual padding condenser HS is also shunted across the section of the condenser used for the long and short wave bands. This capacity is adjusted for the short wave bands, and it has been'found that it should have a very low value. For padding the condenser 3l for operation in the long wave band, the condenser L is shunted across that portion of the coil which is in use only during operation inthe long wave'band. The few turns of winding 40, not shunted by this condenser, are negligible when operating within the long wave band, so that the condenser 4| L is essentially in parallel with the condenser 3|. However, as can be seen from Fig: 1, when the switch 34 is on'contact M for operation in the middle frequency band, the condenser L is in parallel with the condensers 31 and 31', the capacities of which are, therefore, adjusted to form the total series capacity which is required for producing alignment within the intermediate frequency band.

It can thus be seen that -a substantially uniform feed-back coupling is obtained throughout all three of the wave bands.

An important feature of the present invention is that as there is but a single tuning stage in the input to the modulator device, the oscillator frequency is the principal determinate of the frequency to which" the converter is set to respond. This, it can be seen, increases the tuning range of the converter somewhat beyond what would be the case if the condenser 2| determined the range.

As an example, when using a 1,000 kc. intermediate frequency and tuning the oscillator between 3,000 and 9,000 kc., which is a 3:1 ratio, the

incoming frequency which can be received will vary between 2,000 and 8,000 kc., giving a receiving frequency ratio of 4:1.

Fig. 5 shows the modulator of Figs. 1 and 2 arranged for comparison with the circuit shown in Fig. 6.

Fig. 6 shows an alternative form of modularemoved, and the grid leak 48' and grid leak condenser 41' in the grid circuit of the tube l1 havebeen substituted therefor.

Although it is clearthat the specific coils for use in a converter constructed in accordance with the present invention will depend upon the characteristics of various other elements and upon the frequency ranges to be considered, the inductances' used in covering the frequency ranges from 1,740 kc. to 19,400 kc: are shown in Figs. 7-10, and will now be described.

Fig. 7 illustrates the antenna coupling secondary. This secondary is wound on a 1% inch form r by means of spacer 50 and comprises 69% turns of No. 18 B 8i S gauge enameled wire wound 20 turns per inch. The terminal Si is connected to the grid of the tube I1 and the terminal 62 is connected to the ground H. turns and is connected to contact S of switch 24. The tap B5 is taken to include 20% turns and is connected to contact'M of switch 24. The terminal 63 is connected to the antenna coil l5 and is taken 5%; turns from the terminal 52.

The primary of the antenna coupling transformer is wound on inch form 81 and is placed inside the form, Ell of Fig. '7, andspaced therefrom by means of spacer 68. The winding comprises 18 turns of No. 26 B 81 S gauge enameled wire wound 24 turns per inch. The terminals 69 and Ill are connected to the trap circuit l2 and terminal 63 of winding l6, respectively.

The oscillator secondary winding 40, shown in Fig. 9, comprises 43% turns of No. 18 B 8: S 'gauge enameled wire wound on 1% inch form 12, turns per inch. The terminal 13 is connected to contact L of switch 34 and the contact 14 is connected to the grid of oscillator tube 25. The tap I5 is taken 5 turns from the end of coil and the terminal 15 is connected to contact S of switch 34. The terminal 16 is tapped 151/ turns from the end of the coil and is connected to contact M of switch 34.

The feed-back coupling coil 42 and the modulator coupling coils 44 and 45, shown in Fig. 10, are all wound on a inch form llwhich is placed inside of form 12 and spaced therefrom 18. The winding 42 comprises 4 turns of B 8E S gauge enameled wire close wound. Terminals 8i and 82 of winding 42 are connected to the contact L of switch 34 and the oscillator plate condenser 43, respectively. windings 44 and comprise 5 and 4 turns, respectively, of No. 30 B 8; S gauge enameled wire close wound. Winding 45 is spaced inch from winding 42, and windings 44 and 45 are spaced approximately 2 5 inches apart. These coils are connected in series and are connected by terminals 85 and 86 to the cathode of modulator l1 and the modulator bias resistor 46, respectively.

The condensers used have a maximum capacity of 195 microfarads and a minimum capacity of 19 microfarads.

Using the coils just described, the calibrated range of the converter is:

Kilocycles Meters Long wave band 1740-4180 (163-72) Middle wave band- 3800-9075 (79-331) Short wave band..- 8650-19400 (34.8-15.5)

Certain other constants which have been found satisfactory are included:

Resistance 27:250,000 Ohms D0. 29: 25,000 do. Do. 46: 3,000 do. Condenser 36: 450 micromicrofarads Do. 3'7: 1,500 do. Do. 38: 1,500 do. Do. 43: .1 Microfarads D0. 4'7: .1 do.

Although any appropriate tubes may be used a UY224 has been found appropriate for use as modulator I! and W227 has been found to be appropriate for use as the oscillator 25. The

The tap 64 is taken to include 5 determining the frequency power supply device may be provided with the usual UX280, although it is to be understood that any appropriate power supply arrangement may be substituted for that shown.

What is claimed is:

1. In a vacuum tube oscillator for heterodyne reception covering a broad band of wavelengths, subdivided into a short wave band, a middle wave band, and a long wave band, a vacuum tube, a

tunable grid circuit connected to the input of said vacuum tube, and comprising inductance, avariable condenser and a condenser variable in I current of any frequency in a plurality of wave bands, comprising a vacuum tube having plate, grid and cathode electrodes, a grid circuit for to be generated, connected between the grid and cathode, said circuit comprising an adjustable inductance in series with a capacity adjustable in steps, shunted by a continuously variable condenser, a control member for operating said variable condenser, a feed-back circuit between plate and cathode, having an inductance magnetically coupled with said first mentioned inductance, andincluding said adjustable capacity, and switching means, operated by said control member to simultaneously change the values of said adjustable inductance and said adjustable capacity.

3. In an oscillation generator of the thermionic vacuum tube .type, a grid circuit, a frequency determining net work in said circuit, comprising a variable inductance, a capacity variable in steps, and a continuously variable capacity tuning said circuit, and a feed-back circuit, including an inductance magnetically coupled to the first mentioned inductance, and including said capacity variable in steps.

4. In a vacuum tube oscillator for heterodyne reception covering a broad band of wave lengths, an oscillator tube, grid and plate circuits for said tube inductively related to each other and including a common capacitive path, a condenser for tuning said grid circuit, and switching means for altering the effective inductance of said grid circuit and simultaneously altering the capacity of said common capacitive path as the wave length band to which said circuits are adapted to respond is altered.

predetermined portions of said inductance means and capacitance means in said grid and plate circuits to effect large changes in the oscillation frequency. I

6. A system in accordance with claim 1, in which a plurality of variable condensers are provided for tuning the grid circuit of said oscillator,

and selecting means operated simultaneously with said switching means to selectively connect one of said condensers in said grid circuit.

7. A system in accordance with claim 1, in which a plurality of variable condensers'are provided for tuning the grid circuit of said oscillator, selecting means operated simultaneously with said switching means to selectively connect one of the said condensers in said grid circuit, and an adjustable padding condenser arranged in shunt with each of said tuning condensers.

8. In a heterodyne receiving system, an oscillator circuit adjustable to produce oscillations covering a broad wave length band subdivided into a short wave band, a middlewave band and a long wave band, said oscillator circuit comprising an oscillator tube, grid and plate circuits for said tube, said gridcircuit comprising a tuned inductance having one end connected to the grid of said tube and having a middle wave length tap and a short wave length tap, a switch con nected to selectively short-circuit the portions of said inductance below said taps to cause said inductance to respond to frequencies throughout the middle wave length band or the short wave length band respectively, a series alignment condenser for each of the wave length bands, each of said condensers having one side connected to the cathode of said oscillator tube, switching means for connecting the appropriate series alignment condenser in series in the grid circuit, said switching means being connected to and simultaneously operable with the first-mentioned switching means, a variable condenser connected between the grid and cathode of said tube to tune the grid circuit throughout the selected wave length band, a resistance shunted across the series alignment condenser connected in series in the grid circuit between said inductance and the cathode of said tube, and a condenser connected between themiddle wave length tap of said inductance and the cathode side of said variable condenser, whereby it is alternatively placed substantially in shunt with said variable condenser and in shunt with the series alignment condenser used in the middle waveband, andsaid plate circuit including a stopping condenser, an inductance, and the series alignment condenser connected in the grid circuit by said switching means, said last-mentioned inductance being inductively coupled to the grid end of said tuning inductance and connected to the low potential end thereof, whereby the coupling of said ,circuits is altered as the frequency of the band is changed,

9. In a heterodyne receiving system, an oscillator circuit adjustable to produce oscillations covering a broad wave length band, said oscillator comprising a tube; grid and plate circuits for said tube; said grid circuit comprising in series a tuning inductance, a switch so connected as to short-circuit portions of said inductance to cause it to respond to frequencies throughout a plurality of wave length bands, an alignment condenser for each of the wave length bands, and switching means for connecting the appropriate alignment condenser in series in said grid circuit, said switching means being simultaneously operated with said switch, and a variable condenser connected between the grid and cathode of said tube; and said plate circuit including an inductance, inductively coupled to the grid end of said tuning inductance, and the alignment condenser connected in said grid circuit by saidswitching means, said inductances and said alignment condenser being so proportioned that the. coupling between said circuits is essentially electromagnetic at the short wave length end of the band and essentially electrostatic at the long wave length end of the band.

10. An oscillator for covering a broad band of wave lengths, which comprises a vacuum tube, grid and plate circuits therefor, an inductive coupling between said circuits, means for altering the effective inductance of said grid circuit to make large changes in the frequency of said oscillator, a variable condenser in said grid circuit I to vary its tuning, an auxiliary condenser and means related to said inductance altering means for alternatively connecting said auxiliary condenser in circuit as a coupling capacity between said plate and grid circuits or substantially in shunt with said variable condenser.

11. A heterodyne radio-frequency-system for operation over a broad wave band, comprising an oscillator including grid and plate circuits, said circuits each including inductively coupled inductances, and said grid circuit including means for short-circuiting portions of the inductance included therein, one of a plurality of variable condensers, and one of a plurality of coupling condensers, all connected in series, a padding condenser in shunt with each of the variable condensers, means for selectively connecting'one each of said plurality of variable condensers and of said plurality of coupling condensers in said grid circuit, an auxiliary condenser, and means for alternatively connecting said auxiliary condenser in parallel with the coupling condenser then connected in said grid circuit or substantially in shunt with. the variable condenser at that time connected in the circuit.

12. In an oscillation generator of the thermionic vacuum tube type, a grid circuit, a plate circuit, a frequency-determining network in said grid circuit comprising an inductance, a first condenser variable in steps, and a second condenser which is continuously variable for tuning saidv grid, circuit, means for short-circuiting a portion of said inductance for efl'ecting large changes in the frequency of the current generated by said oscillation generator, feedback couplings between grid and plate of said generator and including said first condenser and an inductance electromagnetically coupled to said inductance in said grid circuit, the two couplings together thus provided between said plate and grid circuits being proportioned to provides more uniform output over each of said frequency ranges than would either coupling taken alone.

13. In an oscillation generator including a thermionic vacuum tube, a g"id circuit, a frequency determining network in said grid circuit, said network including inductance variable in steps, a first condenser variable in steps, and a second condenser which is continuously variable for tuning said grid circuit, a feedback circuit including said first condenser and an inductance electromagnetically coupled to said first-named inductance, and means for simultaneously varying said first condenser and said first-named inductance in steps to eifect large changes in the frequency of said oscillation generator.

14. In an oscillation generator including a thermionic vacuum tube, a grid circuit, a frequency-determining network in said grid circuit, said network including inductance variable in steps, a first condenser variable in steps, and a second-condenser which is continuously variable including said first condenser and an inductance electromagnetically coupled to said first-named inductance, and means for simultaneously varying said first condenser and said first-named 1nductance in steps to effect large changes in the frequency of said oscillation generator, the step variations of said first condenser and of said inductance being so proportioned that said first condenser is more effective as a feedback coupling' for the lower frequencies than as a feedback coupling for the higher frequencies.

15. An oscillation generator comprising a vacuum tube having a grid circuit,. a frequencydetermining network in said grid circuit, said network including inductance means adjustable in steps, capacitance means adjustable in steps and a continuously adjustable condenser for tuning said grid circuit, afeed-back circuit including inductance means electromagnetically coupled to said first-named inductance means, and means for adjusting said first-named inductance means in steps to effect large changes in the frequency of said oscillation generator and for simultaneously adjusting said capacitance means for adjusting the coupling between said feed-back circuit and said frequency-determining circuit.

16. In an oscillation generator including a thermionic vacuum tube, a grid circuit, a frequency-determining network in said grid circuit, said network including inductance variable in steps, a first condenser variable in steps, and a second condenser which is continuously variable for tuning said grid circuit, a feedback circuit including said first condenser and an inductance electromagnetically coupled to said first-named inductance, and means for simultaneously varying said first condenser and said first-named inductance in steps to effect large changes in the frequency of said oscillation generator, the step variations of said first condenser and of said inductance being proportioned to cause said first condenser to serve as the principal feedback coupling for the generation of the lower frequencies and to cause said inductance coupled to said first-named inductance to serve as the principal feedback coupling for the generation of the higher frequencies.

1'7. An oscillation generator comprising a vacuum tube having a grid circuit, a frequencydetermining network in said grid circuit, said networkincluding inductance means adjustable in steps, a continuously adjustable condenser for tuning said grid circuit, a feed-back circuit including inductance means electromagnetically coupled to said first-named inductance means, capacitance means in series with a plurality of said inductance steps, means for adjusting said first-named inductance means in steps to effect large changes in the frequency of said oscillation generator, and thereby simultaneously adjusting said capacitance means to adjust the coupling between said feedback circuit and said frequency-determining circuit.

18. In an oscillation generator of the vacuum tube type, adapted to generate oscillations throughout a wide band in frequency and including a tube having plate and grid circuits, a frequency determining circuit, included in the grid circuit of said tube and comprising an inductance, a first capacity and a second capacity, and a feedback circuit, coupled to the plate circuit of said tube and comprising said first capacity, means included in said frequency-determining circuit for continuously varying the generated frequency over a narrow band, and means'for changing in steps the position of said narrow band within said wide band, said last-mentioned means comprising switching means for simultaneously changing in steps the inductance ofsaid frequency-determining circuit and the first ca-, pacity included in both said feedback and Said frequency-determining circuits. I Y 19. An oscillation generator adapted to generate oscillations throughout a wide band of frequencies and including a vacuum tube plate and grid circuits, a frequency-determining network included in the grid circuit of said tube and comprising inductance means, capacitance means and a variable condenser, a feedback circuit coupled to said plate circuit and said network, means comprising said condenser included in said network for continuously varying the generated frequency over a narrow band, and

' means for adjusting in steps the portion of said narrow band within said wide band, said lastmentioned means comprising switching means for simultaneously adjusting said inductance means and said capacitance means in said network.

20. In an oscillation generator of the thermionic vacuum tube type including a cathode and at least two additional electrodes, a frequency determining circuit connected between the cathode and one of said electrodes and comprising a variable inductance, a capacity variable in steps, and a continuously variable capacity tuning said circuit; and a second circuit connected between the cathode and another of said electrodes and including an inductance magnetically coupled to the first-mentioned inductance and including said capacity variable in steps.

21. An oscillation generator for generating a current of any frequency in a plurality of wave bands, comprising avacuum tube having plate, grid and cathode electrodes, a grid circuit for determining the frequency to be generated, connected betweengrid and cathode, said circuit comprising an adjustable inductance in series with a capacity adjustable in steps, shunted by a variable condenser, a control member for operating said variable condenser, a feedback circuit. between plate and cathode, having an inductance magnetically coupled to said first-mentioned inductance, and including said adjustable capacity, and switching means to simultaneously change the values of said adjustable inductance and said adjustable capacity. a

22. An oscillation generator for generating a current of any frequency in a plurality of wave bands, comprising a vacuum tube having plate, grid and cathode electrodes, a grid circuit for determining the frequency to be generated, connected between the grid and cathode, said grid circuit comprising adjustable inductance in series with a capacity adjustable in steps, shunted by a variable condenser, a control member for operating said circuit between plate and cathode, having an inductance magnetically coupled with said firstmentioned inductance, and switching means to simultaneously change the values of said adjustable inductance and said adjustable capacity.

23. An oscillation generator of the thermionic vacuum tube type including grid and plate circuits, a frequency-determining network to tune one of said circuits, said network including a variable inductance, a first capacity adjustable in steps, and a second capacity which is variable;

having variable condenser, a feedback feedback means between said grid and plate circuits including inductive reactance; uni-control means for simultaneously modifying fsaid variable inductance and the value of said first capacity whereby the eflective coupling between the grid and plate circuits is maintained substantially uniformthroughout a broad wave band.

24. An oscillation generator comprising a vacuum tube having grid and plate circuits, a Irequency-determining network for tuning one or said circuits, said network including inductance means adjustable in steps an adjustable tuning condenser and capacitance means acfiustable in steps, a teed-back means between said grid and plate circuits including inductive reactance and at least a portion of said capacitance means, and uni-control means for adjusting said inductance means and for simultaneously adjusting the portion of said capacitance means included in said feedbackv means, whereby the eflective coupling between the grid and plate circuits is main- 

